Rameka seems to think precession is the cause of fade, not OAT. I think, though, that when he says precession, he means torque-free precession. So after the disc corrects itself from torque-induced precession, torque-free precession takes over and begins the normal flight and fade of the disc.
Fade: Fade is not as easy to explain. Fade happens because of a phenomenon called precession. Did any of you play with gyroscope toys when you were kids? Or even things like tops? Precession is the change in the direction of the axis in rotating objects. Precession is not off-axis torque, or in any way associated with it. Precession happens because of a pressure gradient, just like turn. You see, pressure that builds up in the underside of the disc due to slower air flow isn't radially symmetric. There's a point (which differs for different discs, obviously) called the center of lift. To reiterate, the center of lift is generally in a different spot from the center of gravity. This creates an unbalance on the horizontal plane of a disc as seen from behind, just like turn.
Figure 5: 3/4 side views of disc, disc is flying to the left. Air flow is shown in blue again.
Since air slows down in the pocket of the underside of the disc, pressure builds up in this initial area of the pocket, where air is slowest of all. In other words, the leading half of the disc experiences the most pressure; this should seem intuitive. This is the center of lift. Since the disc is spinning clockwise (looking down from above the disc), this pressure's force acts, and then continues to act, for a large portion of the spin, shown above in pink. This causes the starboard wing of the disc to lift up, and, consequently, the port side to dip down (also shown in pink). This causes the disc to fade.